Purpose: The purpose of this paper is to present the characteristics of leadership (style adopted, sources of power exercised and factors affecting leadership) of high school principals in Greece. Design/Methodology/Approach: In total, 235 school principals were surveyed using questionnaires. These questionnaires assessed how often they adopted specific practices while managing their school, in relevance to their educational, managerial and administrative duties. Thus, the researchers were able to assess the leadership style of the principals (transactional or transformational) and the sources of power exercised (reward, punishment, expertise, example and information). Findings: The majority of school principals in Greece prefer the transformational leadership style instead of the transactional one and they frequently exercise the power of information. There is a strong positive link between the transformational leadership style and the tendency to exercise the power of information. Furthermore, it is shown that the leadership skills grow with the educational/managerial work experience of a school principal. Research Limitations/ Implications: The researchers explored the notion of leadership within the context of a centralized educational system, where most critical decisions are taken by central educational administration (e.g. the Greek Ministry of Education). The findings reveal that being a transformational leader in this educational context is not due to the personal characteristics of the school manager (e.g. age, sex, studies). This fact provides insight on issues related to the recruitment/selection and training/development of school managers. Originality/Value: Taking into consideration the fact that there is currently a strong debate in Greece on whether school staff should be evaluated or not (and under what kind of criteria), these findings could be very useful to central education authorities as well as the whole educational community. Furthermore, they contribute toward a better understanding on school principals; what their personal characteristics are (education, work experience), what their leadership style is, how they manage their schools and what obstacles they face. Therefore, it is hoped that in the future, better processes could be followed on recruiting, evaluating and promoting managerial staff within school units.